Enzymatic cleaning of contact lenses is known. For example, Kessler, U.S. Pat. No. 5,169,455, and Kessler et al., U.S. Pat. No. 4,558,586, disclose methods and compositions for cleaning and disinfecting contact lenses which include proteolytic enzymes. Ogunbiyi et al., U.S. Pat. No. 4,690,773, discloses an effervescent enzyme tablet for use in cleaning contact lenses.
Contact lens cleaning compositions, such as enzymatic compositions, particularly those in tablet form, can further include various binders and excipients. Kenjo et al., U.S. Pat. No. 4,731,192, teach chlorite-based contact lens cleaning systems which can include sugars, such as glucose, sucrose and fructose, as oxygen-consuming agents. Tanaka et al., U.S. Pat. Nos. 4,500,441 and 4,259,202, disclose various contact lens cleaning, storage and/or preservative compositions having non-ionic and anionic surfactants, or saccharose fatty acid esters, respectively, as active ingredients. The Tanaka compositions can include polysaccharides such as carboxymethylcellulose, dextran and agar to increase viscosity.
Lad et al., U.S. Pat. No. 4,749,511, disclose contact lens cleaning compositions including proteases in combination with endoproteinases, such as lys-C, together with binders and excipients such as dextran and carboxymethylcellulose.
Winterton et al., U.S. Pat. No. 4,734,222, disclose the use of sucrose in a contact lens cleaning composition. In the Winterton compositions, sucrose particles are used as abradants to physically remove lens soilants.
Since enzymatic activity is affected by the pH of the solution in which the cleaning is effected, it is frequently desirable to use a buffer, such as a neutral borate buffer, during enzymatic cleaning of contact lenses. For example, Huth, U.S. Pat. No. 4,670,178, teaches methods and compositions for cleaning and disinfecting contact lenses. The disclosed compositions can include an enzyme such as papain, together with a buffering agent such as sodium borate, and can be in tablet form. Lad et al. disclose contact lens cleaning compositions which optionally include a boric acid buffer system.
For effective enzymatic cleaning of contact lenses, the desired pH should be maintained throughout the cleaning process. Any excipients used in enzymatic cleaning compositions should not cause a significant drop in the pH of the buffer. Such excipients further should not have an adverse effect on the activity of other ingredients, such as anti-microbial agents, which may also be employed in the compositions. It would be desirable to provide such an enzymatic cleaning composition which is capable of maintaining the pH of a neutral borate buffer.